Among the known dynode structures for photomultiplier tube cages are the box-and-grid dynode structure and the in-line dynode structure. The box-and-grid dynode structure provides excellent electron collection efficiency, but the electron transit time between dynodes leaves something to be desired. The in-line dynode structure provides significantly faster response than the box-and-grid dynode structure.
It is known to combine a box-and-grid dynode structure with an in-line dynode structure to obtain the advantages of both of those arrangements in a photomultiplier tube. Such an arrangement is shown and described in U.S. Pat. No. 5,578,891. However, such tubes necessarily have long profiles. More recently, it has become desirable to shorten the profile of photomultiplier tubes in order to reduce the size of the devices in which they are often used, e.g., scintillation counting devices. One approach to shortening the profile of a photomultiplier tube that utilizes a box-and-grid dynode structure in combination with an in-line dynode structure is shown and described in U.S. Pat. No. 5,598,061.
The need for greater compactness and efficiency of operation in photomultiplier tubes is ever present. Therefore, it would be highly desirable to have a short profile photomultiplier tube that provides the advantages of the box-and-grid and in-line dynode structures, and which provides a better combination of collection efficiency and compactness than the known short profile photomultiplier tube arrangements.